Morphological selection during alloy solidification

Abstract

<p>Directional solidification experiments have been conducted utilizing the succinonitrile-salol transparent metal analog system. The initial transient period prior was scrutinized to clarify current assumptions and adapt the boundary layer model to better reflect experimental conditions. By examining the behavior of the initial onset of planar interface instability a more comprehensive model was developed to include the thermal gradient lag effect. Baseline data was gathered during detailed analysis of the initial transient period. Changes in the planar interface position were shown to be not only dependent on the pulling velocity but also on the movement of the thermal gradient parallel to that pulling velocity. Thus for directional solidification experiments where a constant pulling velocity was imposed, the effective velocity on the interface was shown to ramp up to the pulling velocity as opposed to the assumed constant value. The boundary layer model was modified to incorporate the effects of the thermal gradient movement. A Mullins-Sekerka analysis was performed on the modified boundary layer model and initial wavelengths and time periods until the onset of instability were determined.</p>